Gas chromatograph, specimen capsule for use therein and process for gas chromatography

ABSTRACT

A gas chromatograph capable of analyzing high boiling substances is provided which has a valve for switching the flow of carrier gas at each alternation of the analysis period and the preparation period fixed outside a constant temperature oven. For use in this gas chromatograph, there is provided a specimen capsule which has a ferromagnetic metal piece fixed on a cell containing therein a sample to be analyzed. Another form of specimen capsule usable therein has a sample carried in position by a foil or net of ferromagnetic metal. Also provided is a process for gas chromatography which comprises the steps of placing the said specimen capsule in the vaporizer of the gas chromatograph, vaporizing the sample by means of alternative current induction and conducting necessary analysis on the resultant gases.

United States Patent Nakamura et a1.

GAS CHROMATOGRAPH. SPECIMEN CAPSULE FOR USE THEREHN AND PROCESS FOR GASCHROMATOGRAPHY Filed: Mar. 2, 1973 Appl. No.: 337,712

Foreign Application Priority Data Mar. 9. 1972 Japan 47-24250 Mar. 9.1972 Japan 47-24251 May 8. 1972 Japan .1 47-44583 US. Cl 55/197; 55/386Int. Cl B01d 15/08 Field of Search 55/67. 197. 386

References Cited UNITED STATES PATENTS 10/1962 Brcnncr 55/197 X [451Apr. 22, 1975 3.374607 3/1968 Fisher ct al. 55/67 3.518.059 6/1970 Levy55/67 X 3.550.429 12/1970 MacMurtric et al 55/197 X 3.719.084 3/1973Walker 55/197 X Primary ExaminerJohn Adee Attorney, Agent. or Firm-KurtKelman 1 1 ABSTRACT A gas chromatograph capable of analyzing highboiling substances is provided which has a valve for switching the flowof carrier gas at each alternation of the analysis period and thepreparation period fixed outside a constant temperature oven. For use inthis gas chromatograph, there is provided a specimen capsule which has aferromagnetic metal piece fixed on a cell containing therein a sample tobe analyzed. Another form of specimen capsule usable therein has asample carried in position by a foil or net of ferromagnetic metal. Alsoprovided is a process for gas chro' matography which comprises the stepsof placing the said specimen capsule in the vaporizer of the gaschromatograph. vaporizing the sample by means of alternative currentinduction and conducting necessary analysis on the resultant gases.

1 Claim, 8 Drawing Figures Detector PATENTEDAFRZZIHYS Detector FIG.5FIG.6 FIG 7 GAS CHROMATOGRAPH, SPECIMEN CAPSULE FOR USE THEREIN ANDPROCESS FOR GAS CHROMATOGRAPHY BACKGROUND OF THE lNVENTlON:

This invention relates to an improved pyrolysis gas chromatograph.specimen capsules for use in said gas chromatograph, and a process foranalysis using said specimen capsules.

Generally in gas chromatography. a sample to be analyzed is placed in avaporizer and vaporized by heating or by pyrolysis; the vaporizedcomponents are swept by a carrier gas into a column filled with a columnpacking; the components of the sample vapour are carried through thecolumn at different rates. which are governed by their partitioncoefficient between gas phase and the stationary phase. They emerge fromthe end of the column at different times. Their presence in the emergingcarrier gas is detected by chemical or physical means.

It is desirable that the flow of carrier gas through the column packingshould be also continued while the column is not in service. namelyduring the preparation period, so as to keep the column packing underfixed conditions and protect it against possible degradation. Thecarrier gas flows in different paths during the analysis period andduring the preparation period. The switch of the path of flow iseffected by means of a valve which is placed in the piping of thecarrier gas. In most gas chromatographs. the column and the vaporizerare encased in a constant temperature oven so as to be kept at apredetermined temperature.

In the conventional pyrolysis gas chromatograph, the said switchingvalve is placed between the vaporizer and the column and, during theanalysis period. the vaporized components of the sample are carried bythe carrier gas from the vaporizer to the analyzing column via thevalve. It is therefore, necessary that the valve be placed inside theconstant temperature oven and maintained at the constant temperature, sothat the sample is prevented from being condensed while passing throughthe valve.

The switching valve. is required to incorporate compressible packings ofa rubbery material which serve the purpose of sealing. To satisfy thepurpose, these parts are made of heatproof plastics such as, forexample. Teflon. Even Teflon that has properties most suited to thepurpose cannot withstand temperatures higher than 170C. Thus. thetemperature at which the constant temperature oven maintains theanalyzing column is limited to the highest temperature that theaforementioned parts can withstand.

As concerns the injection of a sample into the vapor izer of the gaschromatograph, one known method accomplishes the injection by taking thesample in a micro-syringe. piercing the needle of this syringe through arubber septum placed to close the entrance to the vaporizer andinjecting the sample into the vaporizer.

when this method is applied to analyzing a volatile substance mingledwith an involatile substance such as, for example, a solvent in a paint.the vaporization of the volatile component occurs first and requires aconsiderable length of time. Consequently, the sample tends to disperseprior to arrival at the column or it is found to be quite difficult toinject the entire sample to the column. There is another disadvantagethat the residue of the sample cannot be extracted after completion ofthe analysis and it is left to contaminate, the vaporizer and thecolumn.

In other methods. the sample is injected into the vaporizer andthermally decomposed therein by the action of heat. There is known. forexample. a method comprising the steps of having a sample solutiondeposited on the surface of a ferromagnetic metal wire about 0.6 mm indiameter and about 20 mm in length, drying the solution, inserting thewire into the vaporizer. exposing the wire to alternative currentmagnetic field thereby inducing it to radiate heat thereby pyrolyzingthe sample deposited on the wire. Since this method requires the sampleto be deposited on the surface of the wire. the applicability of thismethod is limited to liquid samples or to solid samples which can bedissolved with solvents into solutions. The method is not applicable tosolid insoluble samples. When a given solid sample is converted into aliquid sample by the use of a suitable solvent. the liquid sample isdeposited on the wire and subsequently dried free of the solvent. Fromthe practical point of view. however. thorough removal of the solventcontent from the deposited sample is an impossibility. The gas producedfrom the deposited sample by pyrolysis. therefore, entrains the solventcomponent. This means that the chromatogram obtained by this method doesnot represent accurate analysis of the solid sample in the formthoroughly free from foreign matter.

The amount of the sample solution which is deposited on the wire mustalso be considered. Even if the solution to be deposited is the same, itis impossible to have exactly the same amount of solution deposited onall the wires in use. In the case of an excess of deposit. the recordingof the results of analysis becomes impracticable because the peaksprotrude over the edge of the chart paper. One same solution isdeposited on a plurality of wires and the results of analysis conductedon each wire are recorded. therefore, there is involved the troublesomework of making proper adjustment on each wire so that the peaks do notprotrude over the edge of the chart paper. The amount of sample thusdeposited on the wire is quite small. In the case of an operation inwhich mass spectrum is simultaneously performed using a massspectrometer connected next to the gas chromatograph, therefore. theamount of the sample on the wire is not sufficient, making it impossibleto carry out the mass spectrometric identification.

It is a primary object of this invention to provide a gas chromatographadapted so that the path for forwarding the vaporized components ofsamples produced by pyrolysis can be elevated to high temperatureswithout reference to the packing and other similar material used in theswitching valve.

It is another object of this invention to provide a specimen capsule foruse in gas chromatograph, which permits accurate analysis of thevolatile substances contained in high boiling substances and furtherprovide a process for analysis using the said specimen capsale.

It is still another object of the present invention to provide aspecimen capsule for pyrolysis which eliminates the necessity of asolvent even where the sample to be analyzed happens to be a solidsubstance and which is also usable where the sample is a liquidsubstance and further to provide a process for the analysis using saidspecimen capsule.

Yet another object of this invention resides in providing a specimencontaining a constant amount of sample.

SUMMARY OF THE INVENTION This invention relates to a gas chromatographwhich enables any high boiling substance to be analyzed as desired. Inthe conventional gas chromatograph. the valve designed for switching thepath of the flow of carrier gas at each alternation of the analysisperiod and the preparation period is positioned midway between thevaporizer and the column and is enclosed in the constant temperatureoven. The gas chromatograph according to this invention has thisswitching valve disposed outside the constant temperature oven in frontof the vaporizer so that the vaporized sample will not flow through thisvalve. This invention also relates to a specimen capsule for use in thisgas chromatograph and to a process for the analysis using said specimencapsule.

To be specific, in one embodiment of the specimen capsule, a cell madeof galss or a substance with a relatively low melting point such as highmolecular substance is fitted with a piece of ferromagnetic metal at onepart thereof so that the test specimen is prepared by placing a givensample in this cell. Then, the prepared specimen is inserted into thevaporizer of the gas chromatograph. On exposure to alternative currentinduction. the ferromagnetic metal piece is elevated in temperature tothe point of breaking the cell, with the result that the componentswhich have been vaporized out of the sample by this time are swept bythe carrier gas into the column and are subjected to determination.

In another embodiment, a foil or net made of the said ferromagneticmetal is used to contain the sample directly. A capsule is formed of afoil of the ferromagnetic metal and the specimen is prepared by placingtherein a liquid or solid sample. The specimen thus prepared is theninserted in the vaporizer of the gas chromatograph and exposed toalternative current induction so that the ferromagnetic metal is heatedto the extent of radiating heat and causing pyrolysis of the sample intoa gaseous state. The gases thus produced from the sample are forwardedby the carrier gas into the column, wherein it is subjected todetermination.

Other objects and characteristics of the present invention will becomeapparent from the consideration of the further description of theinvention to be given in detail hereinafter with reference to theaccompanying drawings.

BRIEF EXPLANATION OF THE DRAWING I and nets made of ferromagnetic metal.

DETAILED DESCRIPTION OF THE INVENTION The gas chromatograph of thisinvention will be explained with reference to FIG. 1.

In the diagram, 1 denotes a constant temperature oven, 2 a vaporizerdisposed within the constant temperature oven and intended to vaporizeor pyrolyze a sample and 3 an analyzing column and disposed inside thesaid oven 1 next to the said heater compartment, i.e. vaporizer 2.

The vaporizer may be a quarts tube, for example, which has an opening tothe outside of the constant temperature oven. The said opening is keptclosed at all times during operation with a septum 13. The septum 13 isremoved when the specimen is inserted, when the interior of thevaporizer is cleaned or when the system is being prepared for analysisoperation.

In the present invention, a pipe 4 for forwarding the carrier gas to thevaporizer 2 is provided outside the constant temperature oven wiht aswitching valve 5. A pipe 6 for forwarding the carrier gas containingthe separated components of the sample from the column 3 to a detectoris provided inside the constant temperature oven 1 with a tee coupling7. The aforesaid valve 5 and this tee coupling 7 are connected to eachother by a pipe 8 which runs parallel to the vaporizer 2 and the column3. Said vaporizer 2 is exposed to an alternative current magneticinduction field generated by oscillator 10. The said pipe 8 is providedinside the constant temperature oven 1 with a dummy column 9 which isdesigned to balance the flow rate resistance.

The said dummy column 9 is formed so as to provide the same amount ofresistance to the passage of gas as the column 3. Consequently, possibledifference in the volume of carrier gas being forwarded is minimizedwhen the gas is flowing through the column and when it is flowingthrough this dummy column. This enhances the stability of operation ofthe entire system. The switching valve 5 has a structure of theso-called three-way valve in which the path for the gas is shaped likethe letter T. The forked coupling 7 has the structure of a T-shapedpipe.

The gases which may be used as the carrier gas in this invention are NHe, etc.

The manner in which the switching valve 5 in the system of thisinvention is actually operated will be described in detail.

The valve 5 is a three-way valve of the kind frequently found in commonuse. FIG. 1 illustrates the valve 5 in the state which it assumes whilethe system is in the preparation period. During the preparation period,the carrier gas flows from the valve 5 to the tee coupling 7 via thepipe 8 which contains the dummy column 9. The flow of carrier gas isdivided by the tee coupling 7 into two flows, one to the vaporizer 2 andthe other to the concentration detector. By this flow of carrier gas,the column 9 has its column packing protected against possibledegradation.

When the operation is to be switched to the analysis period, thethree-way valve 5 is switched so that the carrier gas will flow throughthe pipe 4 and the flow of the gas to the pipe 8 will be stopped.Consequently, the

carrier gas flows through the vaporizer 2 and enters thecolumn 3 whileentraining the vaporized components of the sample. In the column, thecomponents are separated from one another by the column packing. Then,they are forwarded sequentially from this column and swept to theconcentration detector.

An auxiliary piping containing a reference column 11 within the constanttemperature oven is incorporated in the present gas chromatograph forthe purpose of maintaining the accuracy of analysis at a high level.

In the gas chromatograph of the present invention. the switching valve 5is positoned in front of the vaporizer 2 and outside the constanttemperature oven as already described. The vaporized sample is notallowed to pass through this valve under any condition. Therefore. thesample can be heated to as high a temperature as desired withoutreference to the kind of material of which the valve or its interiorparts are made.

Owing to this innovation. the present invention has made possible theapplication of the technique of gas chromatograph to substances withhigh boiling points.

An explanation will now be given of the specimen capsule of thisinvention which permits accurate analysis selectively of the volatilesubstances in a mixture with involatile substances and to a process foranalysis using the said specimen capsule.

FIG. 2, FIG. 3 and FIG. 4 illustrate preferred embodiments of thespecimen capsule of the present invention. Referring to FIG. 2. l4denotes a cell made of glass or a polymer of a high molecular substanceand IS a piece made of a ferromagnetic metal and pierced through thebottom of the said cell to complete the specimen cap sule. A givensample 16 is poured through the hole 17 into this specimen capsule andthe hole is sealed to form the specimen.

FIG. 3 showns a specimen formed by charging the sample 16 into aspecimen capsule having cell 14 made of glass or some other highmolecular material. inserting the piece 18 of ferromagnetic metalthrough the hole and finally sealing the hole. The specimen capsuleshown in FIG. 4 is formed by winding a wire 19 of ferromagnetic metal inthe shape of a coil or ring around the cell I4 made of glass or somehigh molecular material after the sample 16 has been charged in the celland the hole sealed.

The specimen capsules described above are invariably prepared by formingcells of glass or some high molecular material. hermetically containinggiven samples in the cells. and attaching pieces of ferromagnetic metalto one part of such cells. As a matter of course, the shapes of thespecimen capsules and those of the pieces of ferromagnetic metal are notlimited to those of the illustrated embodiments. The high molecularsubstance of which the cell is made is desirably such that it will notproduce any complicated pyrolysis product. Examples of high molecularsubstances satisfying this requirement are polystyrene, polyethylene,polypropylene and polymethylmetaacrylate. Now a description will begiven of a process for analysis using the specimen capsules of thisinvention. The specimen capsule described above is inserted into thevaporizer and held there until the volatile components of the sample arecompletely gasified. Thereafter the specimen cap sule is exposed toalternative current induction. Consequently. the ferromagnetic metal iselevated in temperature and reaches Curie point temperature. Because ofthe heat, the cell of glass or high molecular material held in contactwith the ferromagnetic metal is broken or fused, with the result thatthe vaporized components of the sample contained in the cell are all atonce released into the vaporizer. The involatile components of thesample held within the cell are not in the least allowed to leak out ofthe system. The components which have thus been released in thevaporizer are carried by the carrier gas into the column andsubsequently swept into the detector for desired determination. TheCurie temperature is 770C for iron. 358C for nickel and 596C for analloy consisting of 60% of nickel and 40% of iron. for example. Theferromagnetic metal for the specimen capsule may be selected from amongthe metals and alloys just mentioned plus nickel-iron alloys,nickelcobalt alloys and other ferromagnetic alloys.

The process of analysis by this invention utilizing the specimen capsuleof this invention has an advantage that all the volatile components ofthe sample are thoroughly volatilized and subjected to analysis and theresidue of the sample can be removed from within the vaporizer aftercompletion of the analysis. Another advantage of the present process isthat the residue from the volatilization continues to remain within thecell and, therefore. finds no opportunity to smear the interior of thevaporizer or the column.

An explanation will now be given of a specimen capsule for use in gaschromatograph. which is suited for pyrolysis by alternative currentinduction heating of samples with high boiling points such as. forexample high molecular substances. and particularly solid substancesresistant to all solvents. and also to a process for the analysis usingaid specimen.

FIG. 5, FIG. 6, FIG. 7 and FIG. 8 are preferred embodiments of specimencapsules of the present invention. Referring to FIG. 5, 20 denotes afoil of ferromagnetic metal having a very small thickness of the orderof 0.05 mm and 21 a sample which is wrapped in the said foil. In thiscase. the sample is a solid substance.

In FIG. 6, a specimen capsule 22 is formed of a foil offerromagneticmetal. This specimen capsule is suited for the analysis of a liquidsample. It can. of course, be applied to analysis of a solid sample.

FIG. 7 and FIG. 8 show samples 25 and 26 wrapped in foils 23 and 24respectively. In the case of these two embodiments, the samples arelimited to solid substances. The foils of ferromagnetic metal describedin the above specimen capsules may be replaced by thin nets made offerromagnetic metal. These nets, however, are not suitable for analysisof liquid samples.

Further. the specimen capsules may be prepared in structures combiningfoils and nets of ferromagnetic metal. A specimen capsule may be formed.for example, by placing a given sample on a foil of ferromagnetic metaland then covering the sample with a net.

FIG. 5, FIG. 6, FIG. 7 and FIG. 8 merely show a few preferredembodiments of the specimen capsules of the present invention. Thespecimen capsules according to this invention are not limited to theshapes illustrated therein. Examples of other shapes the specimencapsules of this invention may assume include those formed by wrapping afoil of ferromagnetic metal around a given sample. by enclosing a samplewith a net of ferromagnetic metal. by bending a foil or net mentionedabove and inserting a sample inside the fold, and by placing a sample ona foil or net produced in the shape of a plate.

When any of the specimen capsules described above is mounted in thevaporizer of the gas chromatograph and then exposed to alternativecurrent induction, the ferromagnetic metal piece is inductively heatedand the sample is pyrolyzed into gaseous components, which are dispersedthroughout the interior of the vaporizer. By a known method previouslydescribed, the gases are swept by the carrier gas to the column. Thecomponents of the sample vapour are carried through the column atdifferent rates, which are governed by their par tition coefficientbetween gas phase and the stationary phase. They emerge from the end ofthe column at different times. Their presence in the emerging carriergas is detected by chemical or physical means. As the ferromagneticmetal used in the specimen capsule of this type, iron, nickel.nickel-iron alloys nicke]cobalt alloys. etc. may be used as alreadydescribed in earlier sections dealing with the specimen capsules for usein the analysis of volatile samples and the process for analysis usingsuch specimen capsules. Satisfactory selection has only to take intoaccount the suitability to the kind of sample to be analyzed.

The specimen capsules and the process of analysis according to thepresent invention can use a solid sam' ple in its unaltered form for thepurpose of analysis and, therefore dispense with the treatment ofdissolving a solid sample in a solvent which is indispensable for theconventionally known alternative current induction heating technique.Further, this invention has a great merit of permitting very easypreparation of specimen capsules containing required sample. addition toa decided advantage that it can be employed for the analysis of liquidsamples.

We claim:

1. A gas chromatograph comprising in combination:

A. a constant temperature oven;

B. a carrier gas introducing pipe;

C. a vaporizer having an entrance for sending a sample thereinto towhich said carrier gas introducing pipe is connected within saidconstant temperature oven for vaporizing said sample and for mixing theresultant vapor with the carrier gas introduced from said introducingpipe and means for discharging the mixed gas out of said vaporizer;

D. an analyzing column disposed inside said constant temperature ovennext to said vaporizer and having a column packing therein for receivingmixed gas discharged from said vaporizer. separating the sample intocomponents by means of said column packing and means for sending saidcomponents outside said analyzing column one after another;

E. a tee coupling disposed inside said constant temperature oven next tosaid analyzing column;

F. a three-way valve disposed at said carrier gas introducing pipe andoutside said constant temperature oven, said three-way valve having anentrance for receiving carrier gas and two exits, one for sending thecarrier gas in the direction of said vaporizer and the other for sendingthe carrier gas in another direction; and capable of being switched ineither di' rection;

G. a system having a dummy column within said constant temperature ovenby which said tee coupling and three-way valve are connected with eachother:

H. a detector disposed outside said constant temperature oven to whichsaid tee coupling is connected for detecting the components sent fromsaid analyzing column; and

l. a system having a reference column within said constant temperatureoven.

l l l l

1. A gas chromatograph comprising in combination: A. a constanttemperature oven; B. a carrier gas introducing pipe; C. a vaporizerhaving an entrance for sending a sample thereinto, to which said carriergas introducing pipe is connected within said constant temperature ovenfor vaporizing said sample and for mixing the resultant vapor with thecarrier gas introduced from said introducing pipe and means fordischarging the mixed gas out of said vaporizer; D. an analyzing columndisposed inside said constant temperature oven next to said vaporizerand having a column packing therein for receiving mixed gas dischargedfrom said vaporizer, separating the sample into components by means ofsaid column packing and means for sending said components outside saidanalyzing column one after another; E. a tee coupling disposed insidesaid constant temperature oven next to said analyzing column; F. athree-way valve disposed at said carrier gas introducing pipe andoutside said constant temperature oven, said three-way valve having anentrance for receiving carrier gas and two exits, one for sending thecarrier gas in the direction of said vaporizer and the other for sendingthe carrier gas in another direction, and capable of being switched ineither direction; G. a system having a dummy column within said constanttemperature oven by which said tee coupling and three-way valve areconnected with each other; H. a detector disposed outside said constanttemperature oven to which said tee coupling is connected for detectingthe components sent from said analyzing column; and I. a system having areference column within said constant temperature oven.